eLFH - Heat and Temperature Flashcards

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1
Q

Temperature dependent enzymatic reactions mechanism

A

Increase in temperature leads to reacting molecules gaining kinetic energy

Increases likelihood of collision between enzyme and substrate

Thus increases rate of reaction

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2
Q

Explanation for there being an optimal temperature for temperature dependent enzymatic reactions

A

There is a temperature at which an enzyme’s catalytic activity is greatest

Above that temperature, enzyme structure begins to denature

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3
Q

Optimal temperature for temperature dependent enzymatic reactions

+ exception to this

A

37.0 degrees Celsius

Except enzymes in testes which function optimally at slightly lower temperature

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4
Q

Energy definition

A

Ability to do work

Can be mechanical, chemical, electrical or thermal

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5
Q

Heat (or heat energy) definition

A

Total energy of molecular motion in a substance

Cannot be directly measured

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6
Q

Heat equation

A

Equation for Kinetic energy

Kinetic energy = 1/2 Mass x Velocity^2

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7
Q

Factors which Heat / Heat energy depends on

A

Kinetic energy of molecules of a substance

Physical state of the substance

Number of molecules in the substance (i.e its mass)

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8
Q

Temperature definition

A

Average kinetic energy of atoms which make up a substance

When temp is measured in Kelvin, it is directly proportional to average kinetic energy of molecules in the substance

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9
Q

Relationship between heat energy and temperature

A

Temperature is measure of likelihood that one substance will transfer heat energy to another

Eg. Iceberg has higher amount of heat energy than pan of boiling water (due to its mass) but boiling water is higher temperature and would transfer heat energy to iceberg

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10
Q

Specific heat capacity definition

A

Amount of heat energy required to raise temperature of 1 kg (a unit mass) of a substance by 1 Kelvin (a unit temperature rise)

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11
Q

Specific heat capacity Equation

A
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12
Q

Units of specific heat capacity

A

kJ / kg / K

can also be as kcal / kg / K

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13
Q

Conversion of kJ to kcal

A

1 kcal = 4.18 kJ

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14
Q

Heat capacity definition

A

Amount of heat energy required to raise the temperature of a given OBJECT by 1 Kelvin

I.e Heat capacity = Specific heat capacity x Mass of object

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15
Q

Units of heat capacity

A

kJ / K

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16
Q

Heat transfer from one object to another equation

A

Amount of heat transferred = Mass x Change in temperature x Specific heat capacity

17
Q

How to calculate temperature change when blood / fluid transfused

A

Amount of heat gained by infusion = amount of heat lost by body (amount of heat transferred)

Therefore can rearrange equation for new temperature (note change in temperature if temp for warmer object is Old temp - New temp, and for cooler object is New temp - Old temp)

18
Q

Heat transfer definition

A

Passage of energy from a warmer object to a cooler object

19
Q

Methods of heat transfer

A

Radiation 40%
Convection 30%
Evaporation 20%
Respiration 10%
(Conduction - minimal, 3-5%)

Royal College Exam Room Chat

20
Q

Reasons for conduction being a limited area of heat loss for patient in operating theatre

A

Air around patient is poor heat conductor

Table is well insulated

Contact area between patient and table relatively small

21
Q

Conduction mechanism

A

Heat transfer due to collision of molecules of two substances

Molecules’ kinetic energy transferred from higher temp substance to lower temp substance

22
Q

Convection definition

A

Transfer of heat by circulation through gas or liquid

23
Q

Convection mechanism with patient in operating room

A

Patient on table surrounded by air
Air warmed by conduction of heat from patient
As air increases in temp, becomes less dense and rises
Replaced by less dense cooler air
Cycle repeats creating convection current

Continues until equilibrium of temperature reached

24
Q

How radiation differs from convection and conduction

A

Does not require matter to transfer heat (eg method of sun heating the earth)

25
Q

Radiation mechanism

A

All objects above 0 Kelvin emit radiation as electromagnetic waves

Amount radiation emitted vs absorbed is a function of the object’s temperature

Waves falling within infrared spectrum are felt as heat

26
Q

Stefan-Boltzmann Law

A

Relates total amount of radiation emitted by an object to its temperature

27
Q

Evaporation mechanism of heat loss

A

Latent heat of vaporisation is taken from body to vaporise water / liquid

Can be described in terms of the other methods of heat loss
E.g Conduction from body to fluid causing evaporation. heat carried away by convection

28
Q

Evaporation heat loss from patient in theatre

A

Sweat or antiseptic solution evaporating from skin

Fluid evaporates from exposed moist internal body cavities

29
Q

Respiration heat loss

A

8% humidification
2% warming of inspired gases

Occurs via combination of other modes of heat transfer